One image-forming device well known in the art includes a photosensitive member on which a latent image is formed when exposed to light, an exposure unit having an exposure surface on which a plurality of light-emitting elements is arrayed along a scanning direction of the photosensitive member for exposing the photosensitive member, and an image-forming unit for forming an image on a recording medium that corresponds to the latent image formed on the photosensitive member. The light-emitting elements is arrayed on the exposure surface of the exposure unit. With this type of image-forming device, the light-emitting elements expose the photosensitive member based on image data to form a latent image on the photosensitive member corresponding to the image data. Subsequently, the image-forming unit configured of a developing unit forms an image on paper or another recording medium corresponding to the latent image formed on the photosensitive member, thereby forming an image on the recording medium that corresponds to the image data.
In order to form precise images on the recording medium, it is important that the exposure unit in this type of image-forming device be positioned accurately in relation to the photosensitive member. Japanese patent application publication No. 2000-181165, for example, proposes a method of positioning the exposure unit relative to the photosensitive member in which protrusions provided on the exposure surface of the exposure unit are fitted into recessions formed in the photosensitive member.